Perrysburg journal. (Perrysburg, Wood Co., O. [Ohio]) 186?-1965, 1887-05-13
THE SOULS WINDOW.
Something About the Wonders
and Beauties of the Eye.

and Beauties of the Eye.
It's Complex Structure In tho Lower AMI
mals-Thc Birds Third EyclId-Union o
the simple and Comp ound In Insects.
Amidst all the marvcls which the
world of nature offers TO the reflective
and obscrvant mind, there are few
which surpass in interest the wonder.
revealed by II study of the mechanism
of sight in the animal kingdom. An
exhaustive study of comparative anat.
omy is by no means necessary TO real
ize these wonders; in fact, we require
TO be reflective ms regards obvious and
familiar details, rather than learned in
scientific terms and anatomical discov-
cries. No very extensive knowledge
of the, structure of the eye, for instance,
is necessary to grasp the full signifi-
cance of the fact that the views obtain
able from the top of st. Pnul's Cathc-
dral or the dizzy pinnaclcs of the Alps
enter the eye through an aperture of
about an cigth of an inch diameter,
and are reproduced in the interior of
the eye on surface averaging the size
of II siNpcncc, from which the size,
shape, color. position, and general
popularity of every object within range
are accurately conveyed to the brain.
This is only one of the ordinary won
ders of the human eye, but shares the
fate of many others in that it seldom
occupies moments thought-no more
thought, in fact, than we bcstow upon
the varieties of sight in the lower ami
mails and the lessons we may learn
from them.
Most of us, in these days of cheap
science manuals, arc familiar with the
general structure of our OWL eyes and
the rudimentary principles of optical
science; and we are so accustomed TO
look upon this particular plan of con-
struction rs the only one by which
vision can be accomplished, that it is
impossible not TO feel astonishcd when
observation discloscs the extraordinary
variety of structural arrangement,
which are to be found in the dcscend
ing scale of animals. In completely
and minutencss of detail, the eye OF
man and the higher animals surpasses
all others; yet its structure may be said
TO explain itself, and to be compare.
lively simple plan, when regarded in
connection with the laws of optics. II
is exactly such rs might be imagined
MS consequence of known laws OF
light transmission and known proper.
. ties of matter. A first glimpse, there,
fore, into the structure of the eyes OF
the lower or invcrtebrate animals is
somewhat pcrplcXing, owing to the ap-
parent contradictions met with; for the
seemingly simple plan of the mammal
eye is lost in II diversity of external
form and internal structure which is
truly marvellous; in some eases, the
elements considered to be essential are
apparently missing; and in others, adj
ditions are found which have no coun-
terpart in eyes supposed to be more
perfect
A little reflection will, however, show
that these diversities of structure,
wherever met with, are necessary to
the particular mode of life which their
possessor was designed to lead in the
ranks of creation. In almost all mann
mails for instance, below the Primates,
n third eyelid-or, as it is called, the
''nictitating" membrane - is found,
commodiously folded up in the inner
corner of the eyeball, ready at any in
slant to sweep across its surface. This
is found in the eyes of all birds, and of
such quadruples as require it, its use
being to wash the eye free from any
foreign particles with the help of the
lachrymal humor, and to defend it
from sudden injuries. 1t is not alto
gether an Opaque membrane, and there
fore, when brought into play by birds
flashing through the air, or flying
straight upwards in the full glare of
the rays of the sun, it prevents the en-
trance of dust or other injurious mat
ter, protects the eye from too strong n
light, and at the same time does not
interfere with sight. The motion of
this membrane is performed in Curl
Gus manner; there are not two antago-
nistic muscles, one pulling forward
and the other backward, as
one might imagine, but only
one muscle, attached by n
tendon to the membrane. The nicti-
tating membrane itself is an elastic
substance, capable of being drawn out
by force like piece of elastic, and re-
turning to its former position when the
force is removed. The muscle which
exercises this force is one of the most
marvellous mechanisms to be found in
nature. Placed at the back of the eye,
it is passed through loop formed by
another muscle, and there infected as il
it were round pulley. This peculiar
ity, necessary for the rapid action
which is required, is one which has
many advantages. In order that the
membrane could be drawn over the
whole eye, longer muscle than could
be extended within the compass at the
base of the eye was required. A greater
length in smaller compass is obtained
by ne cord of the main muscle making
an angle, and the whole action con.
triyed TO n nicely by the angle, instead
Of being round a fixed pivot, being
round a loop formed by another muscle,
with tho result, that whenever tho sec.
ond muscle contracts, II suddenly
twitchcs tho frat muscle at the point o.
tandea, and thereby produces the rapie